Midsummer Management of Pests and Pollinators

It’s summer and organic farmers across the U.S. are in the thick of managing weeds and pests. Right now, many of you are getting ready to till out crabgrass, treating crops to control flea beetles or squash bugs, or maybe wishing you had chosen a different cover crop or crop rotation. When making decisions about these management practices, you have the ability to dramatically affect – for better or worse -populations of beneficial insects that play pivotal roles in crop pollination and pest management. By understanding some basic principles of native bee biology, nesting habits, and the toxicity of various organic-approved pesticides, farmers can balance crop management strategies with the needs of resident wild bees and other beneficial insects.

Organic does not mean benign

Insecticides are usually harmful to beneficial insects and their use should be minimized whenever possible. Even some organic-approved pesticides can have devastating effects on native bees. To reduce these negative effects make sure that your Integrated Pest Management plan incorporates the habitat needs of pollinators.

When insecticides can’t be avoided, choose the least toxic option available. By properly calibrating equipment, using the most targeted spray equipment, and spraying during appropriate weather conditions, farmers can reduce the risk of pesticides or pesticide drift to resident bee populations.

– Choose liquid formulations over dusts, as the dusts are long-acting and can become trapped in the pollen-collecting hairs of bees.

– Be aware of the commonly used organic pesticides that are particularly harmful to native bees (pyrethrins, Rotenone, Beauveria bassiana , and spinosad).

Harnessing beneficials

Native bees and the natural enemies of crop pests need access to pollen and nectar-rich floral resources throughout the growing season in order to thrive. There are many ways to adjust current farm management practices to increase the forage available on your farm. For example, when developing cropping systems or rotations, consider how you can maximize the diversity of bee-pollinated crops in order to provide more abundant forage opportunities throughout the season.

Similarly, it is useful to think beyond one year. You may have an abundance of pumpkin or sunflower in one year, and be building up a population of wild bees near that crop. However, if the next year those crops are not available within the foraging range (say 750 feet) of where the offspring of those bees emerge, they will not continue to increase in number. Cover crops are frequently used to build soil tilth and fertility and control weeds. Choosing bee-friendly flowering cover crops, such as lacy phacelia, buckwheat, clover, or alfalfa, and allowing these cover crops to bloom, provides additional nectar and pollen resources.

This bumble bee is benefiting from the blooms of lacey phacelia used as a cover crop at Villicus Farms in Havre, MT. Photo: Jennifer Hopwood / Xerces

Allowing weeds – only species that aren’t noxious or hosts for pest insects – to flower along field edges, roads, or irrigation ditches can also provide a food source for beneficial insects. Similarly, consider allowing some un-harvested crops to bolt before plowing them under. When combined, all of these practices can
increase the floral resources available on your farm.

Look down!

Approximately 70% of native North American bees nest in tunnels under the ground, and abundant populations have been documented nesting in sunflower and pumpkin fields, and under orchards. When deep tillage is employed to manage field weeds, ground nests and
developing bee larvae can be destroyed. This is particularly relevant for farmers who grow crops in the squash family (cucurbits).

Squash bees in the genus Peponapois have coevolved with cucurbit plants and almost exclusively visit their flowers. These bees tend to nest at the base of the squash plant, between 6 and 12 inches below the ground. Farmers who discover squash bees living in their squash and melon fields could take steps to protect them by plowing at shallower depths (less than 6 in) or investigating the use of no-till options. Similarly, using mulch such as plastic, woodchips, and straw can limit nesting opportunities and inhibit bees from emerging from their nests. We have seen squash bees nesting happily under pumpkin plants growing in plastic mulch where the holes cut in the plastic were at least 1 square foot in size, allowing the bees to find clear ground under the plants.

Squash bees nest in the ground where Cucurbit crops are grown. Tilling practices may negatively impact the abundance of these specialist pollinators. Photo: MaxPixel

These options may not be practical for every farm operation. However, by paying close attention to the natural rhythm of your farmscape and noting the effect that various farm practices have on resident beneficial insects, attracting and protecting pollinator populations can increase not only a farm’s sustainability, but its productivity, too.

This article was written by Ashely Minnerath and Mace Vaughan. It originally appeared in the Summer 2014 issue of Rodale Institute’s New Farm. New Farm is a quarterly publication given to members of Rodale Institute’s Organic Farmers Association. To become a member, visit rodaleinstitute.org/ofa.

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